The Hidden Blade Assassin's Creed in Depth

I believe I have found an alternative to grab move, so it very well may be possible to kill Washington at least a few times in the game.

Just replayed that mission a little while ago. I was both surprised and amused to see Washington in that scene, talking to

Also afterwards, when he's lying on the ground. If you restart from that checkpoint and look close enough, you can see him fall to the ground. I guess the devs were too lazy to have him in a lying down position, so they had him collapse, and the ragdoll physics took care of the rest.

Back to this.
This certainly looks possible. Here are some observations I made.
In sequence eight when you kill the target at the end George Washington IS there. It even shows a health bar with "George Washington" right next to it. Just look at this video, you can tell it's him.
http://www.youtube.com/watch?feature=player_detailpage&v=kQ3IYXevLwU#t=322s
I think Hickey is programmed to fight his two bodyguards before killing Washington. What might work is killing Hickey when he delivers the finishing blow on Washington. Something similar was mentioned by ACFangirl.

Also after the game. I believe you can move him to his death with a horse. Washington continually moves and stands still. While moving he moves out of your way if you're on a horse. There's some water nearby to lead him to.

There's also that part in sequence 9. Like I mentioned before, the first time playing that I talked to him after the scene two more times and he wasn't invincible anymore, but still had unlimited health. After that when I replayed that I couldn't talk to him after the scene. Perhaps it was like an interactive conversation that you can do only once in the game.

And there's also... heh heh heh. Lets just say there's one time in the game he's not invincible or has unlimited health, and there's no penalty for killing him because it shouldn't be possible. My lips are sealed for now.